Hello Shelby,

Several factors may have contributed to the browning of boxwood leaves, including insect damage, diseases, and environmental stress.

Insect pests could be leaf miners, psyllids, small jumping insects, and/or boxwood mites. More information at this link:

https://www.canr.msu.edu/news/boxwood_insect_pests

Many diseases may affect boxwood, including boxwood blight. More information at this link:

https://extension.psu.edu/boxwood-diseases

Environmental factors that may cause the leaves to turn brown include winter desiccation and cold damage. If the shrubs are located near a sidewalk where salt is spread during the winter, salt damage can occur. Winter desiccation of boxwood was prevalent this past winter, and with proper care, plants can often recover.

You are dealing with the box tree moth in the caterpillar stage. Also, being from Oakland County, you are in a quarantine zone.

IMPORTANT! - BEFORE YOU DO PROTECTING YOUR BOXWOODS

I highly recommend sending your images via email to the MSU Plant & Pest Diagnostics Lab.

Their email is <personal data hidden> - Please include your first and last name.

The experts there can also provide you with the best treatment options.

The lab will notify you if they require a sample to be sent.

The lab may also ask for additional images. So be prepared.

Their website is at this link:

Plant & Pest Diagnostics (msu.edu)

Their Contact Information is at this link:

Contact Us - Plant & Pest Diagnostics (msu.edu)

This link will explain the details on submitting a sample to the MSU Plant & Pest Diagnostics Lab:

Submit Samples - Plant & Pest Diagnostics (msu.edu)

Protecting your boxwoods:

If you are in or around the quarantine zone, you can use a preventative pesticide spray to protect your boxwoods, or if you have an identification of box tree moths and need to treat them. We recommend applying bifenthrin (several ready-to-use products available at the garden center) or any pyrethroid insecticide for homeowner use in late July and early September to control all life stages. Pyrethroid insecticides are those where the active ingredient ends in thrin, for example, cyfluthrin, permethrin, resmethrin, cypermethrin, lambda-cyhalothrin, and sumithrin. Use With Caution

Broad-spectrum insecticides are effective but can harm beneficial insects:

Pyrethroids (e.g., bifenthrin, permethrin, cyfluthrin)

Fast acting and widely available

Can disrupt natural predators and pollinators

Use only when necessary and avoid spraying during bloom. More information at these links:

Insecticide Options for Box Tree Moth Management - Integrated Pest Management

Box Tree Moth: Management Guide

Carbaryl (Sevin) and Acephate (Orthene)

Effective but highly toxic to non-target insects

May cause secondary pest outbreaks – More information at this link:

Insecticide Options for Box Tree Moth Management - Integrated Pest Management

Recommended Low-Toxicity Options

Alternatively, homeowners can spray a Bacillus thuringiensis (Bt) product once every two weeks. However, Bacillus thuringiensis is not an effective control for larger caterpillars, eggs, or adults. Bt is a bacterium that kills insects when ingested. There are subspecies of Bt that affect specific types of insects; the subspecies kurstaki specifically targets caterpillar larvae. Look for product labels that say Bacillus thuringiensis subsp. Kurstaki (Btk).

For homeowners, the most environmentally considerate sprays include:

Bacillus thuringiensis kurstaki (Btk)

A biological insecticide that targets caterpillars specifically

Minimizes harm to pollinators and other beneficial insects

Must be ingested by actively feeding larvae to be effective

Available in products like Dipel Pro DF, Javelin, and Deliver - More information at these links:

Insecticide Options for Box Tree Moth Management - Integrated Pest Management

Box Tree Moth: Management Guide

Spinosad

Derived from natural soil bacteria

Effective against caterpillars and has low toxicity to bees when used properly

Found in products like Entrust and Conserve - More information at this link:

Insecticide Options for Box Tree Moth Management - Integrated Pest Management

Application Tips

Apply sprays when caterpillars are small and actively feeding—typically in late July and early September in Michigan. More information at this link:

What growers and landscapers need to know about box tree moth - Landscaping

Use targeted spraying to reduce drift and protect nearby pollinator habitats

Consider using pheromone traps for early detection and monitoring – More information at this link:

Box Tree Moth: Management Guide

If you’re looking for a product at your local garden center, start with a Btk-based spray or Spinosad. These are often labeled for caterpillar control and are safer for beneficial insects.

Finally, check out "Beyond Boxwood: Alternative Landscape Shrubs for Michigan Gardeners" by Lindsey Kerr and Caitlin Splawski, Michigan State University Extension, published on March 13, 2025. Pests like the box tree moth are prompting homeowners to wonder what they can plant that will provide a similar look and feel to boxwood in their gardens. Information at this link:

Beyond boxwood: Alternative landscape shrubs for Michigan gardeners - Gardening in Michigan

I hope this helps!